mod_pubsub_serverinfo: Detect existence of pub/sub node Instead of blindly trying to create the pub/sub node to publish items to, a service discovery query is performed to check if node creation is required. Added various bits of warn and debug logging, to give a user better feedback if and why something is failing.

module:depends("cloud_notify_encrypted");
module:depends("cloud_notify_priority_tag");
module:depends("cloud_notify_filters");